Conventional vehicle closure panels, such as mini-van sliding doors and lift gates, carry a latch assembly that includes a latch member that cooperates with a striker on the vehicle body to retain the panel in a closed position. A manually operated lever or the like is provided to enable a user to release the latch member, thereby enabling the panel to be moved into an open position.
In addition, it is known in the art to provide such latch assemblies with a power operation feature to ensure that the panel is securely and tightly closed. More specifically, these latch assemblies have a power actuator that functions to cinch the panel from an initially closed position to a fully closed position. Typically, the way that these power operated latch assemblies work is that the panel is moved in a closing manner, either manually or under power, towards and into an initially closed position whereat the latch member cooperates with the striker to retain the panel in that position. Then, power is supplied to the power actuator, which responsively moves the latch member in a cinching action to move the panel into its fully closed position. During this cinching action, a motor within the actuator drives the latch member so that it cooperates with the striker to fully close the panel.
To unlatch and open the panel, the user simply actuates the lever to release the latch member, as in conventional latch assemblies. The problem with the powered latch assembly arrangement is that such movement of the latch member back-drives the actuator motor, thereby creating resistance and making such movement somewhat difficult. To remedy this problem, a clutch assembly may be used to uncouple the latch member and the actuator motor, thus obviating the back driving problem. One type of clutch assembly that it would be desirable to use in this context is an electromagnetic clutch assembly. The use of an electromagnetic clutch assembly is desirable as a result of its low cost and reliable performance. From a commercial standpoint, the design of such an electromagnetic clutch assembly must be compact enough for use in the motor vehicle. Further, the material and manufacturing costs of the electromagnetic clutch assembly must be kept relatively low in order to keep the overall costs of the latch assembly at a competitive economic level.
The use of a stamped coil casing for an electromagnetic clutch is preferred because stamping allows the casing to be manufactured relatively inexpensively at a high production rate. However, the use of a stamped coil casing creates a problem with the flux of the magnetic field. Specifically, the overall cross-sectional area of the base wall decreases towards the center thereof. As a result, the base wall provides significantly less cross-sectional area for the flux to flow through at the center thereof than at the radial outer edge thereof. This creates an area of low permeability towards the center of the base wall, which in turn restricts the overall intensity of the magnetic field. Stated differently, the base wall creates a "bottleneck" towards the center thereof. One way to eliminate this bottleneck and increase the field intensity would be to increase the thickness of the base wall, thereby increasing its effective cross-sectional area. However, this results in the overall thickness of the casing being increased. This is undesirable because it increases the overall weight and manufacturing costs associated with the casing.
Alternatively, the casing could be manufactured only with the base wall thereof being provided with an increased thickness. However, this alternative construction cannot be stamped and thus any cost-savings realized by stamping would be lost.